This invention relates to a method for integrity and immobilization enhancement for an absorbent member, and more particularly to a method for applying a foamable movement obstruction agent to an absorbent member which is suitable for use in an absorbent core for a disposable absorbent article.
Absorbent cores which comprise porous members, such as fibrous batts or foamed structures, are well known in the art. Such cores can imbibe liquids, such as discharged body fluids, both by an absorption mechanism wherein fluid is taken up by the porous material itself and by a wicking mechanism wherein fluid is acquired by, distributed through and stored in the capillary interstices. One means for improving the absorbency characteristics of such porous structures is to incorporate therein superabsorbent material, such as polymeric gelling material (also referred to as hydrogel-forming material superabsorbent polymers, etc.) which imbibe fluid. The superabsorbent material serves to retain fluid such as discharge body liquids. An absorbent structure of this type wherein hydrogel-forming materials in particulate form are incorporated into fibrous webs is disclosed in Weisman and Goldman, U.S. Pat. No. 4,610,678, issued Sep. 9, 1986. The combination of superabsorbent materials with foamed structures is, for example, described in U.S. patent application Ser. No. 09/041,930, filed Mar. 13, 1998.
The improvement in absorbency provided by incorporation of absorbent gelling materials has permitted the realization of absorbent articles, such as disposable diapers, which employ relatively thin absorbent cores and which are, therefore, relatively thin products.
Notwithstanding the existence of absorbent cores as described above, there remains a need to provide absorbent cores which reduce and preferably eliminate the phenomena referred to as gel-on-skin. Gel-on-skin is the situation where absorbent gelling materials escape from the absorbent core and travel through the bodyside liner or topsheet of the absorbent article where they come into contact the wearer""s skin.
In one class of prior art continuous lay down operations, fibers and superabsorbent materials are mixed together in a continuous web. The continuous web is then cut into individual absorbent members or cores. The individual absorbent members are then placed between a liquid pervious topsheet and a liquid impervious backsheet to form an absorbent article. However, this configuration provided an unsatisfactory product as absorbent gelling material easily penetrated through the topsheet creating unacceptable amounts of gel-on-skin.
One solution to the above continuous lay down operation, was to place another web, such as a tissue or nonwoven web on top of the continuous web and then cut both the tissue and continuous web into individual members comprising the core and the tissue. The individual members were then placed in the product with the tissue positioned between the topsheet and the absorbent core substantially preventing absorbent gelling material from escaping from the uppermost surface of the absorbent core and thus reducing the amount of gel-on-skin.
However, when for example, the tissue and the continuous web are cut into individual members, the ends of the absorbent core are left open, i.e., the ends of the absorbent core are not covered by the tissue, allowing absorbent gelling material to escape through the ends of the absorbent core.
Similarly, gel-on-skin can occur, if the absorbent articles are formed discretely, i.e. if individual cores are formed for example on a lay-down screen or a lay-down drum, such a described in EP-A-0.478.182. Such cores can be transferred to carrier like tissues or non-wovens to further be integrated into absorbent articles, and such cores also can exhibit before, during or after enveloping as well as during use an undesirable degree of superabsorbent particles being released from the end zones thereof.
Further, gel-on-skin can occur, when foamed materials are combined with superabsorbent materials, such as in U.S. patent Ser. No. 09/041 930, filed Mar. 13, 1998. In such designs, the foam material can be in particulate form, and can be mixed with the superabsorbent material, or the foamed material may be in a layered or sheet like form, and the superabsorbent can be attached thereto.
Hence, it is an object of this invention to provide method of improving the integrity and the immobilization of superabsorbent by reducing the mobility of various absorbent member elements of an absorbent article.
Preferably such a method should be versatile and allow readily adjustment to various changes of the design of the article, yet it should be easy to use.
It is a further object of the present invention to achieve such improvements without detrimental effect on the liquid handling capabilities of the article, and even more preferably to improve the liquid handling capability of the article.
The invention is a method for making an absorbent member comprising superabsorbent material, including the step of applying a foamable movement obstruction agent. More particular, it is a method for making an absorbent article including (a) a first step of providing an absorbent member comprising a superabsorbent material and a foamable agent; and then the steps of (b) foaming said foamable agent, and (c) applying said foamable agent to said absorbent member. The sequence of the steps (b) and (c) can be any of either (b) before (c), or (c) before (b), or (b) and (c) simultaneously.
Upon application of this method, the foamable agent provides a movement obstruction means for the superabsorbent material. The superabsorbent material can be particulate, and the absorbent member can further comprise fibrous material, or can comprise open cell polymeric foam material, preferably of the High Internal Phase Emulsion (HIPE) type.
The foamable agent can have a tack or adhesion behavior at least to the superabsorbent and at least during or after the application phase, such as by being an adhesive. The foamable agent can comprise material selected from the group of natural or synthetic polymeric solutions or emulsions. The foamable agent can be a thermoplastic polymer or polymeric composition having a softening point in the range between 50xc2x0 Celsius and 300xc2x0 Celsius, and can be a wax or a composition containing at least 50% by weight of a wax. In an alternative embodiment, the foamable agent can be a thermo-set polymer or polymeric composition, such as by comprising polyurethane compositions, or polyurethane pre-polymers, which are activated by the addition of initiating chemicals, preferably ambient moisture, or initiating energy, preferably heat or radiation. This activation can be achieved simultaneously to the foaming step.
The foamable agent can be applied to the absorbent member directly, or to a substrate, such as a tissue or a nonwoven wrap, which is combined with the absorbent member after the application of the foaming agent.
The foamable agent can be applied to the absorbent member so as to cover major portions of the surface of the member, such as more than 90% of the total surface of said absorbent member.
Alternatively, the foamable agent can be applied to selected regions of the absorbent member, such as to opposing ends in discrete, spaced apart sealing zones. For these designs, the foamable agent preferably covers less than about 25%, preferably less than 10% and even more preferably less than 5% of the total surface of the absorbent member. In such designs, the foamable agent can be applied in a strip along the edge of the absorbent member having a width of less than about 5 cm, preferably of less than 1 cm. The foamable agent can also penetrate into the structure of the absorbent member.
The foamable agent can remain in the foam structure after the article is manufactured, or the foamed structure can collapse or reticulate after it has been foamed and applied.
The absorbent member can be an individual absorbent member, which can further be wrapped with one or more wrapping materials, which can be bonded by the foamable agent to said absorbent member or to themselves